1. Technical Field
The present invention relates a projector, and particularly to a technology of a projector including a cover portion that protects a projection unit.
2. Related Art
A projector that projects light on a screen to display an image includes a light projection system in a housing. The performance of the projection system is significantly degraded in some cases due to dust, dirt, and other factors. To protect the projection system from dust and dirt, a configuration in which the housing includes a light-transmissive cover portion has been proposed (see JP-A-2004-12749, JP-T-2008-522229, JP-A-2008-107801, and JP-A-2008-165202, for example).
Most of the light projected from the projection system passes through the cover portion and is projected on the screen, but part of the light is reflected off the light-incident surface of the cover portion. The ratio of the amount of light reflected off the cover portion to the total amount of light incident thereon, that is, the reflectance, varies with the angle of incidence of the light that impinges on the light-incident surface. The reflectance of the light-incident surface increases as the angle of incidence increases. The light projected from the projection system may impinge on the light-incident surface at a variety of angles. When the reflectance increases, the amount of light that can reach the screen decreases, and the image brightness decreases accordingly. Therefore, among the projection light incident on the cover portion, the projection light incident at a large angle of incidence disadvantageously forms an image having reduced brightness.
To reduce the amount of reflection off the light-incident surface, it is conceivable to form an anti-reflection film (AR coating) over the light-incident surface of the cover portion. In this case, however, a significantly large number of coating layers is required to achieve an anti-reflection capability across a wide range of angle of incidence, resulting in increase in cost.
On the other hand, there is what is called a proximity projection-type projector capable of projecting wide-angle light from a position close to a screen. Since a proximity projection-type projector uses wide-angle light, the range of the angle of incidence of the light incident on the cover portion increases, and hence the projection light tends to be incident at a large angle of incidence. Therefore, a proximity projection-type projector, in particular, suffers from significant reduction in image brightness due to the angle of incidence of the light incident on the cover portion.